Early avian follicular development is characterized by changes in transcripts involved in steroidogenesis, paracrine signaling and transcription

Abstract

The mechanisms associated with follicular activation and early growth are not well understood in avian species. Level of mRNA transcripts involved in steroidogenesis (STAR, HSD3B, CYP11A1, CYP19), paracrine signaling (AMH, BMP2, BMP4, BMP6, KITL, WNT4, and PCSK6) and transcription (SMAD1, SMAD2, SMAD3, SMAD5, SMAD9, FOXL3, FOXL2, NR5A1 (SF1), and WT1) were determined in small avian follicles 0.5, 1, and 2 mm in diameter after oocyte removal. STAR, HSD3B, CYP11A1, CYP19, PCSK6, FOXO3, and KITL mRNA increased 2- to 45-fold, while FOXL2, WT1, and WNT4 decreased 30-90% and NR5A1 did not change as follicles developed from 0.5 to 2 mm. Phosphorylated SMAD2, SMAD3, SMAD1/5/9 and FOXO3 proteins were found in both granulosa cells and oocytes of small (<0.5 mm) and larger (>1 mm) follicles. In contrast, non-phosphorylated FOXO3 protein was found in oocyte and granulosa cells of small follicles, but only in the oocyte of larger follicles. Culture of small avian follicles on the chorioallantoic membrane of chick embryos (in ovo) for 7 days caused changes in transcript levels that were similar to changes observed in vivo. The collective findings suggest that the growth of avian follicles from 0.5 to 2 mm is marked by an increase in steroidogenic capacity, and changes in paracrine signaling that may be important during early avian follicular development. Thus, a number of candidate marker genes were identified, and a method of follicle culture was developed to study early follicular development in a model avian species.

Bone morphogenetic protein 6 promotes FSH receptor and anti-Müllerian hormone mRNA expression in granulosa cells from hen prehierarchal follicles

“…We note that these findings do not exclude the possibility of BMP6 expression by the oocyte. A decrease in the relative expression of both BMP6 and AMH as small follicles progressively increase in size is consistent with the previous reports (Johnson et al 2008a, 2008b, Diaz et al 2011.…”

The avian ovary and follicle development: some comparative and practical insights

“…An inner, perivitelline layer (consisting of the zona pellucida glycoproteins ZP1, ZP2, ZP3, and ZPD) forms between granulosal cells and the oocyte, and this will subsequently support fertilization and acrosome exocytosis (23) as well as serve as a barrier against microbial contamination (see Section 6). Most primordial follicles (approximately 0.05 mm in diameter) remain loosely associated in clusters in a quiescent state until sexual maturation (24).…”

Gene Expression Profiling by RNA Sequencing in Mature/Immature Oocytes of Chicken

“…품종마다 차이가 있으나, 6개령 암탉에서 지름 1∼35 mm가 되는 2,500개 이 상의 난포로 이루어진 성숙한 난소를 관찰할 수 있다 (Johnson, 2012). 난소는 시산 3∼5주 전에 급격한 발달을 시작하는데, 이 시기에 혈액 중에 황체호르몬(Luteinizing Hormone; LH) 의 농도가 증가하면서 난소에서 에스트로겐(oestrogen)과 프 로게스테론(progesterone) 그리고 안드로겐(androgen) 호르 몬의 분비를 자극하여, 간에서 지방과 단백질 합성을 촉진 시킨다 (Asem and Hertelendy, 1983;Diaz et al, 2011). 합성 된 지방과 단백질 등의 난황물질은 난자에 축적되면서 1개 씩 순차적으로 난자가 성숙하게 된다.…”

“…난포의 성숙은 여포 계층 구조를 따라 성장하는데, 보통 3∼5 mm 크기로 자라는 데 3일 정도 시간이 필요하고, 5∼8 mm 자라는데 2 일 정도 가 필요하며, 8 mm에서 마지막 단계인 산란까지 걸리는 시 간은 6일 정도가 소요된다 (Gilbert et al, 1983). 특히 배란 8 ∼10일 전부터 뇌하수체의 성선자극호르몬에 의하여 난황 이 급격히 성장한다 (Diaz et al, 2011) (Findlay, 1993;Chen and Johnson, 1996), 특히 난황 성숙의 마지막 단계인 F 1~F5 단계의 경우, 여러 종류의 스테로이드 호르몬이 복합적으로 작용하게 된 다 (Huang and Nalbandov, 1979;Etches and Schoch, 1984). 최근 연구 결과에 따르면, 호르몬 이외에 gga-miR-375나 ggamiR-217 등 small RNA도 난황 성숙에 관여하는 것으로 밝 혀졌다 (Kang et al, 2013 포유동물에서 난자는 제1 감수분열 전기에 1차 세포 정지 기 상태로, 5∼10개의 원시과립세포(pregranulosa cell)에 둘 러싸여 있으며, 이 상태를 원시난포(primordial follicle)라 한 다 (Gougeon, 1996).…”